Light reflective materials are now commonly applied to a wide range articles and structures for safety and decorative purposes. The so-called "retroreflective materials" are capable of reflecting the bulk of the light rays impinging upon them in a substantially parallel path back toward the source, and are therefore highly effective, particularly to enhance night-time visibility.
A retroreflective material comprised of minute glass spheres embedded in a matrix of synthetic resin has long been commercially available from the 3M Company, of St. Paul, Minn., under the trade designation SCOTCHLITE. Another type of retroreflective element material, commercially available from the Reflexite Corporation of New Britain, Conn., under the trademark REFLEXITE, comprises a molded plastic member having "cube corner" formations thereon, such as disclosed in Rowland U.S. Pat. Nos. 3,684,348; 3,689,346; 3,810,804; 3,811,983; 3,830,682; 3,935,359; 3,975,083; 3,992,080; 4,244,683; and 4,332,847. Also indicative of efforts to use cube corner formations for retroreflective structures are Straubel U. S. Pat. No. 835,648; Hedgewick et al U.S. Pat. No. 3,258,840; and Jungersen U.S. Pat. Nos. 2,310,790 and 2,444,533.
Among the numerous practical applications for such retroreflective materials are included tapes and patches, bands for posts and barrels, traffic cone collars, and the like. Most applications require that the retroreflective structure exhibit a substantial degree of flexibiity, and in many instances it must be capable of withstanding conditions of thermal cycling and physical abuse without undue distortion or damage and over extended periods of time. Although numerous synthetic plastics are known which are entirely suitable for use under such conditions, and which also afford completely adequate levels of flexibility, in many instances they do not exhibit properties that are consistent with optimal retroreflection. On the other hand, a variety of plastics can readily be molded so as to produce precise cube corner formations, and thereby provide structures that are capable of reflecting light with high efficiency; however, such plastics often lack physical characteristics necessary for certain practical applications.
Exemplary of prior art attempts to provide composite retroreflective materials are the following U.S. Pat. Nos.: Hodgson Jr. et al 2,948,191; Butler 3,017,713; Tung 3,934,065; McGrath No. 4,025,159; Brown 4,082,426; Brasfield et al 4,235,512; and White 4,349,598. The Tung patent specifically shows the utilization of retroreflective sheet material formed into a conical sleeve for mounting upon a traffic cone; a cellular retroreflective structure is disclosed in the McGrath patent; and White teaches using cube corner retroreflectors in a composite film structure. Despite the foregoing, a need remains for a retroreflective material in which is combined desirable mechanical properties, such as toughness, stiffness, and flexibility, together with desirable retroreflective properties, such as brightness and control of incidence and observation angles.
Thus, it is an object of the present invention to provide a novel retroreflective laminar sheet material wherein desired mechanical and retroreflective properties are combined in a highly effective and yet uncomplicated structure.
It is also an object of the invention to provide such a material comprised of plastic sheet components selected for their mechanical properties, combined with separately formed retroreflective components selected to afford desirable optical and photometric properties.
A more specific object of the invention is to provide a novel laminar sheet assembly wherein a multiplicity of retroreflective film pieces are disposed between sheets of flexible plastic material in such a manner that the film pieces are protectively disposed within air and water-tight cells, with the resultant assembly exhibiting a desirable level of mechanical flexibility and freedom from distortion.
Yet another object of the invention is to provide a novel retroreflective sheet assembly in which a high degree of flexibility is possible in the choice of component materials, thereby readily permitting the sheeting to be tailored to a wide range of applications.
Additional objects of the invention are to provide novel methods for the production of retroreflective sheet assemblies having the foregoing features and advantages, which methods are relatively uncomplicated and yet highly efficient.